Add the definition for the new return status code defined in UEFI 2.6. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Fu Siyuan <siyuan.fu@intel.com> Reviewed-by: Samer El-Haj-Mahmoud <elhaj@hpe.com> Reviewed-by: Liming Gao <liming.gao@intel.com>